This application is based on and claims priority under 35 U.S.C. xc2xa7119 with respect to Japanese Application No. 11(1999)-327062 filed on Nov. 17, 1999, the entire content of which is incorporated herein by reference.
The present invention generally relates to a brake master cylinder for a automotive vehicle.
Japanese Utility Model Examined Publication No. 2560091 discloses a brake master cylinder having a cylinder body in which is formed a rearward opening cylinder bore. A cap si fixed to the cylinder body at the front side of the cylinder bore to form a cylinder housing with the cylinder body. A first guide member is coaxially disposed in a bore of the cap, and a second guide member is provided in the cylinder bore. A sleeve is positioned in the bore of the cap, a first piston is inserted into the cylinder housing through the bore of the cap and is slidably supported in an axial direction by a bore of the first guide member and a bore of the sleeve, and a second piston is coaxially provided in front of the first piston and is slidably supported in an axial direction by a bore of the second guide member and the bore of the sleeve.
However, in the above-described brake master cylinder, the first guide member is fixed to the bore of the cap, but a rear side of the sleeve is put in the bore of the cap with an O-ring so that concentricity between the bore of the first guide member and the bore of the sleeve deteriorates. Accordingly, the movement of the first piston in the axial direction is not very smooth.
Moreover, with the brake master cylinder constructed in the above-described manner, the second guide member is fixed to the cylinder bore in front of the sleeve, but the sleeve does not engage with the cylinder bore. Thus, the concentricity between the bore of the second guide member and the bore of the sleeve deteriorates. Accordingly, movement of the second piston in the axial direction is also not very smooth.
In light of the foregoing, a need exists for an improved brake master cylinder that is not as susceptible to the disadvantages and drawbacks described above.
A need thus exists for a brake master cylinder whose pistons are bale to move in a relatively smooth manner in the axial direction.
According to one aspect of the present invention, a brake master cylinder includes a cylinder body having cylinder bore with an open rear end, a cap fixed to the cylinder body at an opening portion of the cylinder bore and forming a cylinder housing with the cylinder body, a first guide member coaxially provided in a bore of the cap, a second guide member coaxially provided in the cylinder bore and having a first bore at its front side and a second bore at its rear side, and a sleeve coaxially fitted into the bore of the cap at its rear end and coaxially fitted into the second bore of the second guide member at its front end. A first piston is fitted into the cylinder housing through the bore of the cap and is slidably supported in the axial direction by a bore of the first guide member and a bore of the sleeve. A second piston is provided in front of the first piston coaxially and is slidably supported in the axial direction by the first bore of the second guide member and the bore of the sleeve.
With the brake master cylinder of the present invention, the rear end of the sleeve is coaxially fitted into the bore of the cap and the first guide member is coaxially provided in the bore of the cap, and so concentricity between the bore of the first guide member and the bore of the sleeve can be accurately obtained. Thus, movement of the first piston in the axial direction is smooth. Also, the second guide member is coaxially provided in the cylinder bore and the front end of the sleeve is coaxially fitted into the second bore of the second guide member, and so accurate coaxial concentricity between the first bore of the second guide member and the bore of the sleeve is achieved. Smooth movement of the second piston in the axial direction is thus achieved.
In accordance with the brake master cylinder of the present invention, the sleeve has a front flange portion formed between the cap and the second guide member so that the sleeve is engaged and nipped by the cap and the second guide member at the front flange portion. Out-of-roundness of the bore of the sleeve is thus maintained relatively precise even if the axial force by the nipping is relatively large. Accordingly, movement of the pistons in the axial direction is smooth.
According to another aspect of the present invention, a brake master cylinder includes a cylinder body having a cylinder bore that is open at a rear end of the cylinder body, a cap having a bore and at least partially positioned in the cylinder bore to form a cylinder housing with the cylinder body, a first guide member coaxially positioned in the bore of the cap, a second guide member coaxially positioned in the cylinder bore, and a sleeve having a rear end coaxially fitted into the bore of the cap and a front end coaxially fitted into the bore of the second guide member. A first piston is slidably supported in the axial direction by the bore of the first guide member and the bore of the sleeve, and a second piston is located coaxially in front of the first piston and is slidably supported in the axial direction by the bore of the second guide member and the bore of the sleeve.
In accordance with another aspect of the invention, a brake master cylinder includes a cylinder body having a cylinder bore that is open at a rear end of the cylinder body, a cap provided with a bore and having a front end portion engaging the cylinder bore to secure the cap in place relative to the cap body, a first guide member having a bore and coaxially positioned in the bore of the cap, a second guide member provided with a bore and coaxially positioned in the cylinder bore, and a sleeve having a rear end coaxially fitted into the bore of the cap and a front end coaxially fitted into the bore of the second guide member. The sleeve is provided with a bore and is engaged by the cap and the second guide member so that the sleeve is axially held in place by the cap and the second guide member. A first piston is slidably supported in the axial direction by the bore of the first guide member and the bore of the sleeve, and a second piston is located coaxially in front of the first piston and slidably supported in the axial direction by the bore of the second guide member and the bore of the sleeve.